Skip to main content

Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

See other formats



as in General Methods (7 and 8), the titration of the free acids being made
on the hot (almost boiling) alcoholic solution of the substance with a
standard alcoholic potassium hydroxide solution (about seminormal), while
for the determination of the saponification number the substance is'boiled
with the alcoholic solution for at least two hours on an asbestos card over
the naked flame, the wax being difficultly saponifiable.

More exact determinations may be made by Berg's method, modified
by Bohrisch and Kurschnei : about 4 grams of the wax, 20 c.c.' of xylene
(recently distilled) and 20 c.c. of absolute alcohol (neutralised) are boiled
in a reflux apparatus for 5-10 minutes; titration of the liquid with semi-
normal alcoholic potash (with phenolphthalein) gives the acid number.
A further quantity of 30 c.c. of the same potash solution is then added,
the liquid boiled for an hour, treated with 50-75 c.c. of 96% alcohol (neu-
tralised), heated for 5 minutes longer, and the excess of potash titrated
with seminormal hydrochloric acid (indicator as above) ; the ester number
is thus obtained.

In judging a wax (see later) it is important to know the acid, saponification
and ester numbers, the last being the difference between the first two.

The ratio of ester number to acid number, the so-called ratio value, is also
of importance.

4.  Iodine Number.—As in General Methods, 12.

5.  Refractometric   Reading.—This  is  determined with  the  Zeiss
butyro-refractometer (see Butter, Vol. II, Chapter II) at a temperature of
64°.    To reduce the reading to the normal temperature of 40°, the difference
between 64 and 40, i.e., 24, is multiplied by 0-53 and the product added to
the reading at 64°.

6.  Test for Stearine.—About 3 grams of the wax and 10 c.c. of 85%
alcohol are heated and shaken in a flask until the wax is thoroughly fused
and then left to cool for some hours with frequent shaking ; only the stearine
(and also any resin, see later, 7) remains in solution.   The solution is then
filtered and the filtrate diluted with a large amount of water.    With the
pure wax the liquid remains clear, whereas the presence of stearine (about
i% or more) produces a marked turbidity or a white precipitate, which
may be collected and identified by means of its melting point (53~55°)
and saponification number (about 195), provided of course that Morawski's
reaction indicates that resin is absent.

When resin and other extraneous acid substances soluble in alcohol are
absent, the stearine (S) added to a wax may be calculated from the acid
number found (a) by means of the formula:

100(0 —20)

c _


When a wax or a mixture resembling wax contains stearic acid and
resin, it is well to eliminate these substances immediately by means of 85%
alcohol and co make the other tebts and determinations on the insoluble


7.  Resin (Colophony) .—From 3 to 4 grams of the wax are heated
with dilute alcohol (about 80%), the mass being allowed to cool and filtered,nt.—As in General Methods, 4.